Some Perspective on Rodenticides

By Stella McMillin

Barn owls are common victims of secondary exposure of anticoagulant rodenticides. Photo Credit: Cornell Lab of Ornithology.

Most of the pesticide-related wildlife problems I deal with currently involve rodenticides.  It is not hard to see why – a material that is toxic to rodents is generally toxic to other vertebrates.  Yet, rodents cause a great deal of damage to agriculture and they are household pests, and so the need for rodent control is real.  While we can recommend non-chemical measures be used whenever possible, we also need to be realistic about the continued use of rodenticides so we can continue to play a part in the regulation of these products.

Anticoagulant rodenticides have been the focus of attention lately for good reason.  Several recent studies have shown widespread exposure among predators and scavengers to anticoagulant rodenticides.  Here at the Wildlife Investigations Laboratory, we have received a few hundred carcasses of wildlife that have been killed as a result of these materials, including San Joaquin kit foxes, mountain lions, bobcats, coyotes, red foxes, gray foxes, black bears, kangaroo rats, golden eagles, great horned owls, barn owls, turkey vultures, Cooper’s hawks, red-shouldered hawks, red-tailed hawks, American kestrels, wild turkeys and Canada geese.

The U.S. Environmental Protection Agency and the California Department of Pesticide Regulation are working on regulatory solutions to decrease unintended impacts associated with anticoagulant rodenticide issue.  Regulation is certainly a step in the right direction. However, regulation of one pesticide often increases the use of another pesticide with a similar function.  And so, as rodenticide use evolves, we must remain vigilant in our protection of wildlife.

One rodenticide I’m keeping my eye on is strychnine. In California, we went nearly a decade without any reported cases of wildlife poisoned by strychnine.  Now, in the last couple of years, we’ve had several.  So, what’s going on?  Is it just coincidence or is it due to the increased regulation of anticoagulant rodenticides?

This is a good example of why education about proper use practices is so important.  Certainly some pesticides are more likely than others to cause problems, including those that are extremely toxic, not selective or persistent.  But even the more environmental friendly pesticides can cause problems if they aren’t used properly.  So we keep our eyes open and keep working together to protect wildlife.

Photo credit: Alison Kent, Wildlife Health Center, UC Davis

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